Transient human cortical responses during the observation of simple finger movements: a high-resolution EEG study

Abstract

High-resolution event-related potentials (ERPs) were used to model the hemispherical representation of the transient cortical responses relating to the observation of movement during execution (right or left aimless finger extension). Subjects were seated in front of the observed person and looked at both their own and the observer's hand to receive similar visual feedback during the two conditions. In a visual control condition, a diode light moved at the observed person's hand. A first potential accompanying the movement execution peaked at about +110 msec over the contralateral somatomotor areas. It was followed by a potential (P300) peaking at about +350 msec over the central midline. In contrast, the potentials accompanying the movement observation peaked later over parietal-occipital other than somatomotor areas (N200 peak, +200 msec; P300 peak, +400 msec). Notably, the N200 was maximum in left parietal area whereas the P300 was maximum in right parietal area regardless the side of the movement. They markedly differed by the potentials following the displacement of the diode light. These results suggest a rapid time evolution (approximately 200-400 msec) of the cortical responses characterizing the observation of aimless movements (as opposite to grasping or handling). The execution of these movements would mainly involve somatomotor cortical responses and would be scarcely founded on the visual feedback. In contrast, the observation of the same movements carried out by others would require dynamical responses of somatomotor and parietal-occipital areas (especially of the right hemisphere), possibly for a stringent visuospatial analysis of the motor event.

Figure 1

Data from nine subjects. Grand average waveforms of the event‐related potentials (ERPs). These waveforms refer to representative electrodes of 10–20 of the montage system for the four experimental conditions, i.e., the execution (EXE) of self‐initiated right or left finger movements and the observation (OBS) of right or left finger movements. Also, the grand average waveforms of the EMG activity of the observer and the observed are reported.

Figure 2

Three‐dimensional color maps of movement‐related potentials during the execution of right (RT) and left (LT) movements. The maps refer to the peaks of readiness potential (RP), motor potential (MP), and movement‐related response 1 (MRR1). Color scale: maximum normalized negativity (white) and maximum normalized positivity (violet).

Figure 3

Three‐dimensional color maps of ERPs accompanying the execution and observation of right (RT) and left (LT) movements. The maps refer to N200 and P300 peaks. Color scale: maximum normalized negativity (white) and maximum normalized positivity (violet).

Figure 4

Group means (±SE) of the ERP amplitude (ANOVA). Means refer to a statistical interaction among the factors Condition (EXE, OBS), ROI (Fl, Fr, Cl, Cm, Cr, Pl, Pr), and Component (N200, P300). *Duncan post‐hoc testing, P < 0.05; **Duncan post‐hoc testing, P < 0. 0005. ROIs: Fl, left frontal; Fr, right frontal; Cl, left central; Cm, centromedian; Cr, right central; Pl, left parietal‐occipital; Pr, right parietal‐occipital.

Figure 5

Data from five subjects. Grand average waveforms of ERPs for the conditions of movement observation (OBS) and of displacement of a diode light (LIGHT). The visual stimulus was a ring device worn on the observed person's right hand. The waveforms refer to the main frontal (F3, F4), central (C3, C4), parietal (P3, P4), and occipital (O1, O2) electrode sites of both hemispheres. The grand average waveform of the EMG activity of the observer during the movement observation (OBS) is represented.